blackbutterfly
Emperor
As you can see I'm able to attack China's units and Chinese units attack and pillage my cities...BUT China is an ally. Also, I can't make peace with its city states.
I think this happened in the brief moment the alliance and friendship with China expired, Monty & Qin made a joint war with me. Meanwhile I was in the diplomacy screen and renewed my friendship and alliance with China.
See game save.